1. Cross-Reference to Related Applications
This application is related to the following application assigned to the assignee of the instant invention:
U.S. patent application Ser. No. 433,396 entitled "Stepper Motor Tracking Accuracy Control" by Allan S. Way and Stanley L. Pratt, filed Jan. 14, 1974, now U.S. Pat. No. 4,000,946; and
U.S. patent application Ser. No. 433,397 entitled "Voltage Variab. Digital Clock" by Allan S. Way and filed Jan. 14, 1974, now U.S. Pat. No. 3,895,315.
2. Field of the Invention
This invention relates to chart recording systems, and more particularly to chart recording systems utilized with spectrophotometer or optical density measuring systems.
In spectrophotometer systems as shown and described in the above-identified related applications, an optical characteristic of a sample is measured to provide a signal indicative of the optical characteristic. Although the above-identified applications relate to an optical null infrared spectrophotometer, it is to be understood the principles hereinafter described are equally applicable to an optical system such as an ultraviolet spectrophotometer having a single beam path and a detector.
In either instance a wavelength scanning device is utilized to transmit light of differing wavelengths through the sample to provide an output through the system indicative of the optical characteristic which may be absorbance or transmittance, this output then being recorded as a spectrum of wavenumber or wavelength (abscissa) versus optical characteristic (ordinate) on a chart paper. There are many manufacturers of such instruments and various manufacturers utilize differing chart sizes and formats for the output, some of the charts being dimensioned in metric units and others being dimensioned in English units. In the usual situation where a user already has a particular spectrophotometer, he has derived a standard set of charts or spectrograms giving spectral analysis for known samples. The user then utilizes the standard charts for comparison purposes against unknown samples. In the instance where an operator or user has a particular set of standard charts derived from a given instrument, he is unable to draw a direct comparison with a spectrum derived from another manufacturer's instrument on a one-to-one relation basis if the latter manufacturer's charts employ a different format. Thus, if he utilizes another manufacturer's instrument, he is then required to run a new set of standard charts on known samples for comparison with unknown samples later analyzed on the same instrument.
Furthermore in such instruments the manufacturers provide abscissa scale expansion circuitry as well as ordinate scale expansion circuitry. However, this does not provide the user with the flexibility desired inasmuch as the abscissa scale expansion circuitry is normally desired for use when the spectrum is a given portion of the chart within a certain wavenumber range contains such high density information that certain peaks are not discernible; the user then has the option of selecting an expansion number such as "1X", "2X", etc., which merely drives the chart twice as fast on "2X", thereby spreading out the crowded portion of the spectrum. Similarly, on the ordinate scale, the ordinate expansion is intended to utilize the full Y-axis of the chart paper to provide a magnified version of a portion of the spectrum on the Y-axis in a selected range such as 50 to 100% transmittance, 80 to 100% transmittance or the like. Neither of these scale expansions utilized separately or in conjunction can resolve the problem associated with the various chart sizes and formats in English or metric units of various manufacturers.